Class BloomFilter<T>
 java.lang.Object

 com.google.common.hash.BloomFilter<T>

 Type Parameters:
T
 the type of instances that theBloomFilter
accepts
 All Implemented Interfaces:
Predicate<T>
,Serializable
,Predicate<T>
@Beta public final class BloomFilter<T> extends Object implements Predicate<T>, Serializable
A Bloom filter for instances ofT
. A Bloom filter offers an approximate containment test with onesided error: if it claims that an element is contained in it, this might be in error, but if it claims that an element is not contained in it, then this is definitely true.If you are unfamiliar with Bloom filters, this nice tutorial may help you understand how they work.
The false positive probability (
FPP
) of a Bloom filter is defined as the probability that mightContain(Object) will erroneously returntrue
for an object that has not actually been put in theBloomFilter
.Bloom filters are serializable. They also support a more compact serial representation via the
writeTo(java.io.OutputStream)
andreadFrom(java.io.InputStream, com.google.common.hash.Funnel<? super T>)
methods. Both serialized forms will continue to be supported by future versions of this library. However, serial forms generated by newer versions of the code may not be readable by older versions of the code (e.g., a serialized Bloom filter generated today may not be readable by a binary that was compiled 6 months ago).As of Guava 23.0, this class is threadsafe and lockfree. It internally uses atomics and compareandswap to ensure correctness when multiple threads are used to access it.
 Since:
 11.0 (threadsafe since 23.0)
 Author:
 Dimitris Andreou, Kevin Bourrillion
 See Also:
 Serialized Form


Method Summary
All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods Modifier and Type Method Description boolean
apply(T input)
Deprecated.Provided only to satisfy thePredicate
interface; usemightContain(T)
instead.long
approximateElementCount()
Returns an estimate for the total number of distinct elements that have been added to this Bloom filter.BloomFilter<T>
copy()
Creates a newBloomFilter
that's a copy of this instance.static <T> BloomFilter<T>
create(Funnel<? super T> funnel, int expectedInsertions)
Creates aBloomFilter
with the expected number of insertions and a default expected false positive probability of 3%.static <T> BloomFilter<T>
create(Funnel<? super T> funnel, int expectedInsertions, double fpp)
Creates aBloomFilter
with the expected number of insertions and expected false positive probability.static <T> BloomFilter<T>
create(Funnel<? super T> funnel, long expectedInsertions)
Creates aBloomFilter
with the expected number of insertions and a default expected false positive probability of 3%.static <T> BloomFilter<T>
create(Funnel<? super T> funnel, long expectedInsertions, double fpp)
Creates aBloomFilter
with the expected number of insertions and expected false positive probability.boolean
equals(@Nullable Object object)
Indicates whether some other object is "equal to" this one.double
expectedFpp()
Returns the probability that mightContain(Object) will erroneously returntrue
for an object that has not actually been put in theBloomFilter
.int
hashCode()
Returns a hash code value for the object.boolean
isCompatible(BloomFilter<T> that)
Determines whether a given Bloom filter is compatible with this Bloom filter.boolean
mightContain(T object)
Returnstrue
if the element might have been put in this Bloom filter,false
if this is definitely not the case.boolean
put(T object)
Puts an element into thisBloomFilter
.void
putAll(BloomFilter<T> that)
Combines this Bloom filter with another Bloom filter by performing a bitwise OR of the underlying data.static <T> BloomFilter<T>
readFrom(InputStream in, Funnel<? super T> funnel)
Reads a byte stream, which was written by writeTo(OutputStream), into aBloomFilter
.static <T> Collector<T,?,BloomFilter<T>>
toBloomFilter(Funnel<? super T> funnel, long expectedInsertions)
Returns aCollector
expecting the specified number of insertions, and yielding aBloomFilter
with false positive probability 3%.static <T> Collector<T,?,BloomFilter<T>>
toBloomFilter(Funnel<? super T> funnel, long expectedInsertions, double fpp)
Returns aCollector
expecting the specified number of insertions, and yielding aBloomFilter
with the specified expected false positive probability.void
writeTo(OutputStream out)
Writes thisBloomFilter
to an output stream, with a custom format (not Java serialization).



Method Detail

copy
public BloomFilter<T> copy()
Creates a newBloomFilter
that's a copy of this instance. The new instance is equal to this instance but shares no mutable state. Since:
 12.0

mightContain
public boolean mightContain(T object)
Returnstrue
if the element might have been put in this Bloom filter,false
if this is definitely not the case.

apply
@Deprecated public boolean apply(T input)
Deprecated.Provided only to satisfy thePredicate
interface; usemightContain(T)
instead.Description copied from interface:Predicate
Returns the result of applying this predicate toinput
(Java 8 users, see notes in the class documentation above). This method is generally expected, but not absolutely required, to have the following properties: Its execution does not cause any observable side effects.
 The computation is consistent with equals; that is,
Objects.equal
(a, b)
implies thatpredicate.apply(a) == predicate.apply(b))
.

put
@CanIgnoreReturnValue public boolean put(T object)
Puts an element into thisBloomFilter
. Ensures that subsequent invocations ofmightContain(Object)
with the same element will always returntrue
. Returns:
 true if the Bloom filter's bits changed as a result of this operation. If the bits
changed, this is definitely the first time
object
has been added to the filter. If the bits haven't changed, this might be the first timeobject
has been added to the filter. Note thatput(t)
always returns the opposite result to whatmightContain(t)
would have returned at the time it is called.  Since:
 12.0 (present in 11.0 with
void
return type})

expectedFpp
public double expectedFpp()
Returns the probability that mightContain(Object) will erroneously returntrue
for an object that has not actually been put in theBloomFilter
.Ideally, this number should be close to the
fpp
parameter passed in create(Funnel, int, double), or smaller. If it is significantly higher, it is usually the case that too many elements (more than expected) have been put in theBloomFilter
, degenerating it. Since:
 14.0 (since 11.0 as expectedFalsePositiveProbability())

approximateElementCount
public long approximateElementCount()
Returns an estimate for the total number of distinct elements that have been added to this Bloom filter. This approximation is reasonably accurate if it does not exceed the value ofexpectedInsertions
that was used when constructing the filter. Since:
 22.0

isCompatible
public boolean isCompatible(BloomFilter<T> that)
Determines whether a given Bloom filter is compatible with this Bloom filter. For two Bloom filters to be compatible, they must: not be the same instance
 have the same number of hash functions
 have the same bit size
 have the same strategy
 have equal funnels
 Parameters:
that
 The Bloom filter to check for compatibility. Since:
 15.0

putAll
public void putAll(BloomFilter<T> that)
Combines this Bloom filter with another Bloom filter by performing a bitwise OR of the underlying data. The mutations happen to this instance. Callers must ensure the Bloom filters are appropriately sized to avoid saturating them. Parameters:
that
 The Bloom filter to combine this Bloom filter with. It is not mutated. Throws:
IllegalArgumentException
 ifisCompatible(that) == false
 Since:
 15.0

equals
public boolean equals(@Nullable Object object)
Description copied from class:java.lang.Object
Indicates whether some other object is "equal to" this one.The
equals
method implements an equivalence relation on nonnull object references: It is reflexive: for any nonnull reference value
x
,x.equals(x)
should returntrue
.  It is symmetric: for any nonnull reference values
x
andy
,x.equals(y)
should returntrue
if and only ify.equals(x)
returnstrue
.  It is transitive: for any nonnull reference values
x
,y
, andz
, ifx.equals(y)
returnstrue
andy.equals(z)
returnstrue
, thenx.equals(z)
should returntrue
.  It is consistent: for any nonnull reference values
x
andy
, multiple invocations ofx.equals(y)
consistently returntrue
or consistently returnfalse
, provided no information used inequals
comparisons on the objects is modified.  For any nonnull reference value
x
,x.equals(null)
should returnfalse
.
The
equals
method for classObject
implements the most discriminating possible equivalence relation on objects; that is, for any nonnull reference valuesx
andy
, this method returnstrue
if and only ifx
andy
refer to the same object (x == y
has the valuetrue
).Note that it is generally necessary to override the
hashCode
method whenever this method is overridden, so as to maintain the general contract for thehashCode
method, which states that equal objects must have equal hash codes.  It is reflexive: for any nonnull reference value

hashCode
public int hashCode()
Description copied from class:java.lang.Object
Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided byHashMap
.The general contract of
hashCode
is: Whenever it is invoked on the same object more than once during
an execution of a Java application, the
hashCode
method must consistently return the same integer, provided no information used inequals
comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.  If two objects are equal according to the
equals(Object)
method, then calling thehashCode
method on each of the two objects must produce the same integer result.  It is not required that if two objects are unequal
according to the
Object.equals(java.lang.Object)
method, then calling thehashCode
method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
As much as is reasonably practical, the hashCode method defined by class
Object
does return distinct integers for distinct objects. (The hashCode may or may not be implemented as some function of an object's memory address at some point in time.) Overrides:
hashCode
in classObject
 Returns:
 a hash code value for this object.
 See Also:
Object.equals(java.lang.Object)
,System.identityHashCode(java.lang.Object)
 Whenever it is invoked on the same object more than once during
an execution of a Java application, the

toBloomFilter
public static <T> Collector<T,?,BloomFilter<T>> toBloomFilter(Funnel<? super T> funnel, long expectedInsertions)
Returns aCollector
expecting the specified number of insertions, and yielding aBloomFilter
with false positive probability 3%.Note that if the
Collector
receives significantly more elements than specified, the resultingBloomFilter
will suffer a sharp deterioration of its false positive probability.The constructed
BloomFilter
will be serializable if the providedFunnel<T>
is.It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since
equals(java.lang.Object)
also relies on object identity of funnels. Parameters:
funnel
 the funnel of T's that the constructedBloomFilter
will useexpectedInsertions
 the number of expected insertions to the constructedBloomFilter
; must be positive Returns:
 a
Collector
generating aBloomFilter
of the received elements  Since:
 23.0

toBloomFilter
public static <T> Collector<T,?,BloomFilter<T>> toBloomFilter(Funnel<? super T> funnel, long expectedInsertions, double fpp)
Returns aCollector
expecting the specified number of insertions, and yielding aBloomFilter
with the specified expected false positive probability.Note that if the
Collector
receives significantly more elements than specified, the resultingBloomFilter
will suffer a sharp deterioration of its false positive probability.The constructed
BloomFilter
will be serializable if the providedFunnel<T>
is.It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since
equals(java.lang.Object)
also relies on object identity of funnels. Parameters:
funnel
 the funnel of T's that the constructedBloomFilter
will useexpectedInsertions
 the number of expected insertions to the constructedBloomFilter
; must be positivefpp
 the desired false positive probability (must be positive and less than 1.0) Returns:
 a
Collector
generating aBloomFilter
of the received elements  Since:
 23.0

create
public static <T> BloomFilter<T> create(Funnel<? super T> funnel, int expectedInsertions, double fpp)
Creates aBloomFilter
with the expected number of insertions and expected false positive probability.Note that overflowing a
BloomFilter
with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.The constructed
BloomFilter
will be serializable if the providedFunnel<T>
is.It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since
equals(java.lang.Object)
also relies on object identity of funnels. Parameters:
funnel
 the funnel of T's that the constructedBloomFilter
will useexpectedInsertions
 the number of expected insertions to the constructedBloomFilter
; must be positivefpp
 the desired false positive probability (must be positive and less than 1.0) Returns:
 a
BloomFilter

create
public static <T> BloomFilter<T> create(Funnel<? super T> funnel, long expectedInsertions, double fpp)
Creates aBloomFilter
with the expected number of insertions and expected false positive probability.Note that overflowing a
BloomFilter
with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.The constructed
BloomFilter
will be serializable if the providedFunnel<T>
is.It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since
equals(java.lang.Object)
also relies on object identity of funnels. Parameters:
funnel
 the funnel of T's that the constructedBloomFilter
will useexpectedInsertions
 the number of expected insertions to the constructedBloomFilter
; must be positivefpp
 the desired false positive probability (must be positive and less than 1.0) Returns:
 a
BloomFilter
 Since:
 19.0

create
public static <T> BloomFilter<T> create(Funnel<? super T> funnel, int expectedInsertions)
Creates aBloomFilter
with the expected number of insertions and a default expected false positive probability of 3%.Note that overflowing a
BloomFilter
with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.The constructed
BloomFilter
will be serializable if the providedFunnel<T>
is.It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since
equals(java.lang.Object)
also relies on object identity of funnels. Parameters:
funnel
 the funnel of T's that the constructedBloomFilter
will useexpectedInsertions
 the number of expected insertions to the constructedBloomFilter
; must be positive Returns:
 a
BloomFilter

create
public static <T> BloomFilter<T> create(Funnel<? super T> funnel, long expectedInsertions)
Creates aBloomFilter
with the expected number of insertions and a default expected false positive probability of 3%.Note that overflowing a
BloomFilter
with significantly more elements than specified, will result in its saturation, and a sharp deterioration of its false positive probability.The constructed
BloomFilter
will be serializable if the providedFunnel<T>
is.It is recommended that the funnel be implemented as a Java enum. This has the benefit of ensuring proper serialization and deserialization, which is important since
equals(java.lang.Object)
also relies on object identity of funnels. Parameters:
funnel
 the funnel of T's that the constructedBloomFilter
will useexpectedInsertions
 the number of expected insertions to the constructedBloomFilter
; must be positive Returns:
 a
BloomFilter
 Since:
 19.0

writeTo
public void writeTo(OutputStream out) throws IOException
Writes thisBloomFilter
to an output stream, with a custom format (not Java serialization). This has been measured to save at least 400 bytes compared to regular serialization.Use readFrom(InputStream, Funnel) to reconstruct the written BloomFilter.
 Throws:
IOException

readFrom
public static <T> BloomFilter<T> readFrom(InputStream in, Funnel<? super T> funnel) throws IOException
Reads a byte stream, which was written by writeTo(OutputStream), into aBloomFilter
.The
Funnel
to be used is not encoded in the stream, so it must be provided here. Warning: the funnel provided must behave identically to the one used to populate the original Bloom filter! Throws:
IOException
 if the InputStream throws anIOException
, or if its data does not appear to be a BloomFilter serialized using the writeTo(OutputStream) method.

